Evaluation of Intra- and Interlaboratory Variations in SARS-CoV-2 Real-Time RT-PCR Through Nationwide Proficiency Testing

Abstract

Objective: This study aimed to examine the intra- and interlaboratory variations of cycle threshold (Ct) values using the nationwide proficiency testing for SARS-CoV-2.

Methods: Triplicated strong-positive contrived samples duplicated weak-positive contrived samples, and 2 negative samples were transported to participating laboratories in October 2021.

Results: A total of 232 laboratories responded. All except 4 laboratories correctly answered. Six false-negative results, including 2 false-negatives with Ct values beyond the threshold and 1 clerical error, were noted from weak-positive samples. Intralaboratory variations of Ct values of weak-positive and strong-positive samples were not acceptable (Ct > 1.66) in 17 and 7 laboratories, respectively. High interlaboratory variations of Ct values (up to 7 cycles) for the 2 commonly used polymerase chain reaction (PCR) reagents were observed.

Conclusion: The overall qualitative performance was acceptable; intralaboratory variation was acceptable. However, interlaboratory variations of Ct values were remarkable even when the same PCR reagents were used.